A hybrid vehicle may include an internal combustion engine and an electric machine to propel the vehicle. The engine may output a first torque at wide open throttle and a given air-fuel ratio at a constant engine speed while operating at sea level. The same engine may output a second engine torque at wide open throttle at the same air-fuel ratio at the same constant engine speed while operating at an altitude well above sea level. The first torque may be greater than the second torque because there is more oxygen available at sea level than at a higher altitude. Thus, if a human driver requests a large amount of torque at a higher altitude, powertrain output may be reduced because of reduced engine output. Electric machine output may also be subject to changes in output due to battery operating conditions and electric machine temperature. At higher altitudes, engine and electric machine output inconsistency may be exacerbated because of the coupling between the engine and the electric machine to provide a desired powertrain torque. In particular, a control system may attempt to increase electric machine output to compensate for reduced engine output at higher altitudes, but increased reliance on the electric machine may affect battery state of charge and electric machine temperature. As a result, performance of both the engine and the electric machine may be more inconsistent at higher altitude. As such, a human driving the hybrid vehicle may notice inconsistency in hybrid powertrain output, and the vehicle's driver may find the inconsistency objectionable. Therefore, it may be desirable to provide reduce hybrid vehicle powertrain inconsistency when the hybrid vehicle is operating at sea level or at a higher altitude.
The inventors herein have recognized the above-mentioned issues and have developed a powertrain operating method, comprising: receiving sensor input to a controller; and limiting powertrain output via the controller in response to a ratio of a threshold electric machine torque to a threshold engine torque.
By constraining or limiting powertrain output in response to a ratio of a threshold electric machine torque to a threshold engine torque, it may be possible to provide more consistent powertrain output at sea level and at altitude without having to reduce powertrain output to engine output at higher altitudes. For example, powertrain output may be determined to vary with electric machine and engine output. However, a ratio of threshold electric machine torque to threshold engine torque may be used as a basis for reducing inconsistency related to altitude and electric machine output. Consequently, powertrain output may be limited based on a combination of electric machine output and engine output.
The present description may provide several advantages. Specifically, the approach may reduce powertrain output differences at sea level and higher altitudes, and the benefits may be most significant when the hybrid vehicle is operated at higher altitudes. In addition, the approach may reduce powertrain output inconsistency at sea level or higher altitude without limiting powertrain output to maximum power the hybrid powertrain's engine outputs at higher altitude. Further, the approach may limit powertrain output in response to powertrain output power or powertrain torque.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.